Microwave optical spectroscopy of polyvalent charge states of transition element ions in silicon carbide

Four possible charge states of molybdenum in silicon carbide (SiC) are analyzed: paramagnetic Mo$^{3+}$(4$d^3$), Mo$^{4+}$(4$d^2$), Mo$^{5+}$(4$d^1$), characterized by axial symmetry, and diamagnetic Mo$^{6+}$(4$d^0$). Using high-frequency electron paramagnetic resonance (EPR) and low temperatures for Mo$^{4+}$ with spin $S$ = 1, which is the neutral charge state in the $A^0$ crystal, a positive sign of the fine structure splitting $D$ was established for two quasi-cubic positions k1 and k2: $D$(k1)=3.06 GHz, $D$(k2)=3.29 GHz and the values of $g$-factor are determined: $g_\parallel$ = 1.9787 and $g_\perp$ =1.9811, that is, $g_\perp>g_\parallel$. The contributions of paramagnetic and diamagnetic components in non-phonon lines of optical absorption of Mo$^{4+}$ ions in the near-IR region were separated by magnetic circular dichroism (MCD) of absorption at different temperatures. For the charge state of Mo$^{5+}$(4$d^1$), the off-center position of the substititional impurity in place of the silicon atom was established and superhyperfine (SHF) interactions with ligand nuclei $^{29}$Si and $^{13}$C were determined. A comparative analysis of hyperfine (HF) interactions with odd isotopes of molybdenum $^{95}$Mo и $^{97}$Mo having a nuclear magnetic moment in three charge states is carried out. Due to works using vanadium V$^{4+}$ in SiC for quantum information and communication, since these defects have photoluminescence lines in the transmission window of about 1300 nm, it is shown that in the main transmission window of about 1540 nm, erbium Er$^{3+}$ in SiC is very promising, and we previously managed to introduce Er$^{3+}$ in SiC bulk crystals. It is important that at room temperature a significant decrease in the V$^{4+}$ photoluminescence line in SiC is recorded, whereas for Er$^{3+}$ ions in SiC such a decrease is insignificant and photoluminescence line can be observed up to 400 K.